JP2019171284A - Photocatalyst and photocatalyst electrode for hydrogen generation - Google Patents

Abstract

To provide a photocatalyst allowing for generation of hydrogen from water using a visible light, having excellent hydrogen generation activity, and allowing for improvement of optical electrochemical property of a photocatalyst electrode for hydrogen generation using the photocatalyst.SOLUTION: The photocatalyst is provided which is composed of a composite metal compound having a chalcopyrite type crystal structure and allows for generation of hydrogen from water using a visible light, and in which the composite metal compound contains Cu, S, at least one of Ga and In, and alkali metal as essential components, contains at least one of Zn and Se if needed, and contains alkali metal of 0.001 to 5 mol% based on all metal atoms in the composite metal compound.SELECTED DRAWING: None

Description

  The present invention relates to a photocatalyst capable of generating hydrogen from water using visible light and a photocatalyst electrode for hydrogen generation using the photocatalyst.

  In recent years, the practical use of light energy conversion systems using solar energy has increased in importance from the viewpoint of suppressing global warming and moving away from dependence on depleted fossil resources. In particular, the technology for decomposing water using solar energy to produce hydrogen is not only used in the current oil refining technology and ammonia and methanol feedstock technology, but also in the future hydrogen energy society based on fuel cells. Promising as a hydrogen supply technology.

  In addition, the technology for producing hydrogen from water using light energy is regarded as a technology for converting light energy into chemical energy, but it has not been easy to store the electric energy that has been put into practical use for a long time. For this reason, while advancement of power storage technology is desired, chemical energy such as hydrogen is expected to be dominant energy in energy storage and transportation and energy amount per unit.

  Photocatalysts that generate (generate) hydrogen and oxygen by water splitting are roughly divided into two types for hydrogen generation and oxygen generation. Among them, many metal sulfides respond to long-wavelength light, and there are many proposals as photocatalysts for hydrogen generation.

As a proposal of a metal sulfide-based photocatalyst, for example, in Patent Document 1, as a photocatalyst effective for hydrogen generation, a report on a composite metal sulfide represented by a composition formula Zn _1-2x (CuGa) _x In ₂ S ₄ There is. Patent Document 2 reports a photocatalyst composed of a sulfide solid solution in which a part of Cu or In in CuInS ₂ is substituted with Ag or Ga as a photocatalyst effective for hydrogen generation. In Patent Document 3, as an effective photocatalyst to hydrogen generation, there is a report on a visible light active sulfide solid solution represented by a composition formula _{(CuAg) x In 2x Zn 2} (1-2x) S 2.

Similarly, Non-Patent Document 1 reports a metal sulfide photocatalyst represented by the composition formula Cu _0.8 Ga _0.8-x In _x Zn _0.4 S ₂ as a photocatalyst effective for hydrogen generation.

JP 2009-0666529 A JP 2006-167852 A JP 2005-199222 A

The 92nd Annual Meeting of the Chemical Society of Japan (2012) 1G1-43 “Solar Hydrogen Production Using Mixed Sulfide Photocatalyst of Cu0.8Ga0.8-xInxZn0.4S2”

  Various metal sulfides have been proposed as photocatalysts that can decompose hydrogen using visible light to generate hydrogen. In particular, chalcopyrite, which is a sulfide containing copper, is a solar cell. Many of them are useful as photoresponsive materials including CIGSe (Cu—In—Ga—Se), which is used as However, the photocatalytic properties (hydrogen generation activity) and photoelectrochemical properties of these sulfide materials used for water splitting under visible light irradiation are still not sufficient.

  In view of the present situation, the present invention is a photocatalyst capable of generating hydrogen from water using visible light, has excellent hydrogen generation activity, and photoelectrochemical characteristics of a photocatalytic electrode for hydrogen generation using the photocatalyst It is an object of the present invention to provide a photocatalyst capable of improving the efficiency and a photocatalytic electrode for hydrogen generation.

  In the chalcogenide-based composite metal compound having a chalcopyrite type crystal structure, the present inventors include Cu, S, at least one of Ga and In, and an alkali metal such as Li, Na, K, and Cs as essential components. By containing at least one of Zn and Se as required and containing a specific amount of an alkali metal, the photocatalyst comprising this composite metal compound and the photocatalyst electrode using the photocatalyst emit visible light. It has been found that it exhibits high performance (excellent hydrogen generation activity and photoelectrochemical properties) as a photocatalyst for generating hydrogen from water and a photocatalytic electrode for hydrogen generation. Specifically, the present invention provides the following.

[1] A photocatalyst comprising a composite metal compound having a chalcopyrite type crystal structure and capable of generating hydrogen from water using visible light, wherein the composite metal compound comprises Cu, S, Ga and In At least one of the above and an alkali metal as an essential component, and optionally contains at least one of Zn and Se, and 0.001% of the alkali metal with respect to all the metal atoms in the composite metal compound. A photocatalyst containing ˜5 mol%.

[2] The photocatalyst according to [1], wherein the composite metal compound contains Cu, S, at least one of Ga and In, an alkali metal, and Zn.

[3] A photocatalytic electrode for hydrogen generation having the photocatalyst described in [1] or [2].

  According to the present invention, Cu, S, at least one of Ga and In, and an alkali metal are contained as essential components, and if necessary, at least one of Zn and Se is contained. By using a photocatalyst composed of a composite metal compound having a chalcopyrite-type crystal structure containing 0.001 to 5 mol% with respect to a metal atom, a photocatalyst excellent in hydrogen generation activity and photoelectrochemical characteristics using the photocatalyst An excellent photocatalytic electrode for hydrogen generation can be provided.

XRD measurement result of CGIZS photocatalyst Photoelectrochemical property evaluation result of CGIZS photocatalyst XRD measurement result of CGIZS photocatalyst Photoelectrochemical property evaluation result of CGIZS photocatalyst XRD measurement result of CGIZS photocatalyst Photoelectrochemical property evaluation result of CGIZS photocatalyst XRD measurement result of CGIZS photocatalyst Photoelectrochemical property evaluation result of CGIZS photocatalyst XRD measurement result of CGIZS photocatalyst

  Hereinafter, the form for implementing this invention concretely is shown. 1. 1. Photocatalyst composition and crystal structure 2. production method of photocatalyst; 3. Cocatalyst and surface modification. 4. Method for producing photocatalytic electrode, The hydrogen generation method by photohydrolysis and the evaluation of the photoelectrochemical properties of the photocatalytic electrode will be described in order.

1. Composition and Crystal Structure of Photocatalyst The composite metal compound constituting the photocatalyst of the present invention has a chalcopyrite type crystal structure.
Chalcopyrite is the English name for chalcopyrite CuFeS ₂ which is a golden mineral. This material is an antiferromagnetic semiconductor having a tetragonal crystal structure in which zinc-blende (ZB) structure typified by ZnS is stacked in two layers and Zn is orderedly replaced by two elements of Cu and Fe. All the constituent elements are surrounded by tetrahedrons of other elements, and atoms are connected by a strong covalent bond.

Chalcopyrite structure basically shows the composition of the ABC _2, element composing separately roughly, there are I-III-VI ₂ group type and _{II-IV-V 2} Group type two. In the group I-III-VI type ₂ , the main constituent elements are Cu or Ag, group III is Al, Ga, In, group VI is S, Se, Te, while II-IV-V _{In the} group ₂ type, the group II is Zn or Cd, the group IV is Si, Ge or Sn, and the group V is P or As.

CIGSe (chalcogenide consisting of Cu, In, Ga, Se), which is put into practical use as a solar cell material having a chalcopyrite structure, has a I-III-VI group ₂ type structure, but CIGSe is suitable for the use of sunlight. It is well known as a material having visible light absorption characteristics.

The composite metal compound constituting the photocatalyst of the present invention is the above-mentioned I-III-VI group ₂ chalcopyrite structure, wherein group I corresponds to Cu, group III corresponds to Ga or In, group VI corresponds to S, and the chalcopyrite type It has a crystal structure of

  The composite metal compound having a chalcopyrite crystal structure (hereinafter also referred to as “composite metal compound in the present invention”) constituting the photocatalyst of the present invention is at least one of Cu, S, Ga, and In. And an alkali metal as an essential component, containing at least one of Zn and Se as required, and containing 0.001 to 5 mol% of an alkali metal with respect to all metal atoms in the composite metal compound It is characterized by doing. In addition, it is preferable that the composite metal compound in this invention contains Cu, S, at least one of Ga and In, an alkali metal, and Zn. Moreover, the composite metal compound in this invention may contain metal components other than Cu, S, Ga, In, Zn, and an alkali metal.

  Such a composite metal compound in the present invention has a function of generating hydrogen with high activity by decomposing water under irradiation with visible light by incorporating it as a photocatalyst as it is or in a photocatalytic electrode. That is, the photocatalyst comprising the composite metal compound in the present invention is excellent in hydrogen generation activity as a photocatalyst that generates hydrogen from water using visible light. In addition, a photocatalyst electrode manufactured using such a photocatalyst, for example, a photocatalyst electrode having a current collecting conductor layer on which photocatalysts are laminated has improved photoelectrochemical characteristics.

  The band structure of the composite metal compound in the present invention varies depending on the content of each metal component. In the valence band of the composite metal compound, Cu 3d and S 3p orbitals contribute to band formation, and the composite metal compound conduction band is Ga 4s4p, In 5s5p and Zn 4s4p orbitals. It is supposed to contribute to formation. Since the position of 5s5p of In is located on the noble side with respect to 4s4p of Ga and 4s4p of Zn, the position of the conduction band of the composite metal compound depends on the change in the composition of the three of Ga, In and Zn Change.

The photocatalyst that enables hydrogen generation by water splitting needs to have a potential at the lower end of the conduction band lower than 0 V _RHE , and any of the composite metal compounds in the present invention is considered to satisfy it.

  Here, the present inventors have intensively studied and found that a CGIS (chalcogenide containing Cu, at least one of In and Ga, and S) photocatalysts were compared with those synthesized by a solid phase method. It was found that those produced by the flux method using a eutectic molten salt composed of lithium and potassium chloride exhibit higher activity in photocatalytic properties. Further investigation was conducted to find out the reason, and as a result, the present inventors found out that there is a difference in the amount of alkali metal components contained in the photocatalyst, and reached the present invention. That is, the activity of the photocatalyst is improved when synthesizing by the active addition of alkali metal during the synthesis by the solid phase method in which no alkali metal is present, and the flux using the eutectic molten salt composed of lithium chloride and potassium chloride It was found that lithium remained in the catalyst synthesized by the method.

  In CIGSe (chalcogenide composed of Cu, In, Ga, Se), which is known as a solar cell material having a chalcopyrite type crystal structure, the effect of adding an alkali is known. In the CIGSe solar cell, by using soda lime glass as a substrate, Na ions diffuse into the CIGSe light absorption layer, so that in the CIGSe solar cell containing Na, the open circuit voltage is increased and the conversion efficiency is improved accordingly. There is an excellent effect in terms of performance. The effect of Na ions in CIGSe solar cells is thought to be due to improved physical properties such as improved carrier concentration, but there are various theories as to why such improved properties appear. Support is not enough. Also in the photocatalyst of the present invention and the photocatalyst electrode using the same, the initial process of charge separation into excited electrons and holes by light absorption is assumed to have the same mechanism as the above solar cell, and therefore the effect of similar alkali addition is effective. Although it seems to be expected, there are no documents that have been reported so far.

  The amount of the alkali metal contained in the composite metal compound in the present invention is 0.001 to 5 mol%, preferably 0.01 to 2.5 mol% of the alkali metal with respect to all metal atoms in the composite metal compound. It is. In the present specification, the metal atom in the composite metal compound is a metal atom other than alkali metal and alkali metal, and Se and S are not metal atoms. The content (mol%) of the alkali metal with respect to all the metal atoms in the composite metal compound is determined on a molar basis by the sum of alkali metals / (total of metal atoms other than alkali metals and alkali metals) × 100. Further, the amount of the alkali metal contained in the composite metal compound in the present invention is preferably 1 ppm to 5000 ppm and more preferably 5 ppm to 2000 ppm on a weight basis.

  As the alkali metal contained in the composite metal compound in the present invention, lithium, sodium, potassium, rubidium, cesium and the like are suitably used, lithium, sodium and potassium are more preferred, and lithium is more preferred.

  The details of how these alkali metals are contained in the composite metal compound are not fully understood. For composite metal compounds produced by the flux method, in the production process, the water washing step is usually carried out several times in order to remove the alkali halide remaining after the flux treatment. Therefore, it is considered that the alkali metal may be taken into the crystal lattice in an ionic state. In fact, the XRD measurement of a composite metal compound containing lithium shows that the crystal lattice constant is small, and lithium having an ionic radius smaller than that of other Cu, Ga, In, and Zn metals may be taken into the crystal lattice. It has been confirmed.

  Moreover, the composite metal compound in this invention is a composite metal compound which has a chalcopyrite type crystal structure and is represented by the following formula (1), for example. In addition, when the composite metal compound in this invention is a composite metal compound represented by following formula (1), content (mol%) of the alkali metal with respect to all the metal atoms in a composite metal compound is f / (f + a + b + c + d). It is calculated | required by x100.

_{Cu a Ga b In c Zn d} S 2-e X e Y f ··· (1)
(In the above formula, a, b, c, d, e, and f satisfy the following conditions, X represents Se, and Y represents an alkali metal.
0 <a ≦ 2, 0 <(b + c) ≦ 1.67, 0 ≦ d <2, 0 ≦ e <2, 0 <f <0.1. )

  The content ratio of the components contained in the composite metal compound in the present invention is not particularly limited as long as it has a chalcopyrite type crystal structure. In the formula (1), preferably, 0.2 ≦ a ≦ 1.2, 0.0 ≦ b ≦ 1.0, 0.0 ≦ c ≦ 1.0, 0.0 ≦ d ≦ 1.5, 0.0 ≦ e ≦ 1.0, 0.0001 ≦ f ≦ 0.100, More preferably, 0.4 ≦ a ≦ 1.0, 0.0 ≦ b ≦ 0.8, 0.0 ≦ c ≦ 0.8, 0.0 ≦ d ≦ 1.2, 0.0 ≦ e ≦ 0.5 and 0.0001 ≦ f ≦ 0.050. Moreover, as above-mentioned, content (mol%) of an alkali metal, ie, f / (f + a + b + c + d) * 100, Preferably, it is 0.001-5.0, More preferably, it is 0.01-2.5. is there.

2. Production method of photocatalyst The production method of the photocatalyst of the present invention is not particularly limited. As described above, the manufacturing method is not limited as long as the elemental component and composition of the composite metal compound constituting the photocatalyst and the chalcopyrite type crystal structure are satisfied.

  In the present invention, a physical film forming method such as a solid phase method, a flux method, a solid phase method, or MBE (molecular beam epitaxy method) can be used. In particular, a flux method or MBE film formation is preferably used.

In the solid phase method, as a raw material, a metal sulfide such as cuprous sulfide (Cu ₂ S), gallium sulfide (Ga ₂ S ₃ ), indium sulfide (In ₂ S ₃ ), zinc sulfide (ZnS), or Metal selenides such as cuprous selenide (Cu ₂ Se), gallium selenide (Ga ₂ Se ₃ ), indium selenide (In ₂ Se ₃ ), and zinc selenide (ZnSe) can be used. In addition, as an alkali metal source, a sulfide or selenide, for example, an alkali metal sulfide such as lithium sulfide, sodium sulfide, or potassium sulfide, or an alkali metal selenide such as lithium selenide or sodium selenide is used. Can do. These are usually solids, and are mixed well in powder form.

  The production conditions in the solid phase method include a mixture of raw materials of 600 ° C. or higher, preferably 700 ° C. or higher, more preferably under vacuum or reduced pressure, or under normal pressure and in the presence of an inert gas such as nitrogen or argon. Is produced by heat treatment at 800 ° C. or higher for several hours to several tens of hours. After the heat treatment, it can be used for the production of a photocatalyst or a photocatalytic electrode by performing a treatment such as pulverization after returning to room temperature.

In the flux method, as a raw material, a metal sulfide such as cuprous sulfide (Cu ₂ S), gallium sulfide (Ga ₂ S ₃ ), indium sulfide (In ₂ S ₃ ), zinc sulfide (ZnS), or selenium Metal selenides such as cuprous iodide (Cu ₂ Se), gallium selenide (Ga ₂ Se ₃ ), indium selenide (In ₂ Se ₃ ), and zinc selenide (ZnSe) can be used. These are usually solids, and are mixed well in powder form.

  The flux agent used in the flux method is not particularly limited. For example, metal chlorides such as alkali metal chlorides such as lithium chloride, sodium chloride, potassium chloride, and cesium chloride, and alkaline earth metal chlorides such as calcium chloride, strontium chloride, and barium chloride are preferably used. Of these, lithium chloride, sodium chloride, potassium chloride, and cesium chloride are more preferable, and it is particularly preferable to mix two or more of these chlorides. Since these mixtures show a low melting point, they are preferably used as a fluxing agent.

  For example, a mixture of lithium chloride (melting point 605 ° C.) and potassium chloride (melting point 770 ° C.) forms a eutectic molten salt with a melting point of 352 ° C. at a molar ratio of 59.5: 40.5. A mixture of sodium chloride (melting point 801 ° C.) and cesium chloride (melting point 645 ° C.) also becomes an eutectic molten salt having a melting point of 486 ° C. at a molar ratio of 35:65.

  As the metal chloride used in the flux method, a combination of lithium chloride and potassium chloride is particularly preferable. As a mixed composition of lithium chloride and potassium chloride, the molar ratio of lithium chloride to potassium chloride is preferably 40:60 to 80:20, and 50:50 to 70:30, in that the melting point is lowered. It is more preferable that it is 59.5: 40.5 in that the melting point is the lowest. In this embodiment, as the metal chloride, a mixture of lithium chloride and potassium chloride in a molar ratio of around 59.5: 40.5 is preferably used.

  The amount of the fluxing agent to be used, that is, the amount of the metal chloride is not particularly limited, but is preferably 1 or more and about 20 or less in terms of molar ratio with respect to the amount of the raw material metal sulfide or metal selenide mixture. 5 or more and about 10 times or less are suitable. Within such a range, the heat treatment in the method for producing a composite metal compound or photocatalyst represented by the above general formula can be easily lowered, and the component range of the above general formula can be easily achieved.

  The heat treatment in this embodiment, that is, the temperature at the time of flux is preferably 400 ° C. or higher and 800 ° C. or lower, more preferably 450 ° C. or higher and 750 ° C. or lower.

  The heat treatment time is preferably 0.5 hours or more and 50 hours or less, more preferably 1 hour or more and 30 hours or less, and further preferably 2 hours or more and 20 hours or less.

  The heating rate in the heat treatment is preferably 0.5 ° C./min or more and 20 ° C./min or less, more preferably 1 ° C./min or more and 15 ° C./min or less.

  The temperature lowering rate in the heat treatment in this embodiment is preferably 0.5 ° C./min or more and 20 ° C./min or less, more preferably 1 ° C./min or more and 15 ° C./min or less. In particular, since the temperature drop has a great influence on crystal growth, there are cases where not only the temperature is lowered at a constant speed, but also a device such as holding at a constant temperature in the middle or changing the temperature drop speed in the middle may be effective. Specifically, the temperature is lowered at a temperature lowering rate of 1 ° C./min or more and 15 ° C./min or less, then held at a constant temperature of 300 ° C. or more and 600 ° C. or less for 30 minutes or more and 300 minutes or less, and then 1 ° C. For example, a method of lowering the temperature to near room temperature at a temperature lowering rate of 15 ° C./min.

The heat treatment in the present embodiment can be performed in the atmosphere, and is usually performed at a pressure of 0.1 × 10 ⁵ Pa or more and 2000 × 10 ⁵ Pa or less, for example, 1 × 10 ⁵ Pa or more and 1000 × 10 ⁵ Pa or less. It can be carried out. Such heat treatment can be performed, for example, in an open reaction vessel. Therefore, the heat treatment in this embodiment does not require heat treatment under vacuum, and the metal sulfide or metal selenide used as a raw material and the metal chloride used as a flux agent are closed such as quartz glass tubes and quartz ampule tubes. It is not necessary to perform heat treatment in the reaction vessel of the system, but the atmosphere during the heat treatment or flux in the present embodiment is not particularly limited, and it is in the air or in an inert gas atmosphere, and usually under reduced pressure or vacuum. Any atmosphere is applicable, and heat treatment may be performed in either a closed or open reaction vessel. The atmosphere during heat treatment or flux in this embodiment is preferably in the apparatus, under an inert gas atmosphere, or under vacuum, and more preferably under vacuum.

  After performing the heat treatment (flux), it is preferable to remove the flux agent remaining excessively in the catalyst by washing with water. Since the metal sulfide, metal selenide and the photocatalyst of the present invention are insoluble in water and the metal chloride is soluble in water, the metal chloride which is a flux agent can be effectively removed by washing with water. .

  The amount of water used for cleaning, the number of times of cleaning, the cleaning time, etc. are not particularly limited, and the normal indication is that chlorine is no longer detected in the cleaning water. As a cleaning method with water, for example, using 2 to 20 times the volume of solids per cleaning, the number of cleaning is usually 3 times or more, and the cleaning time is 5 minutes / time or more. It is done. Usually, within such a range, the number of washings can be 6 times or less and the washing time can be 60 minutes or less / time.

  After washing, it is usually dried. The drying method is not particularly limited, but it is desirable to remove moisture without applying much heat load. It is preferable to dry at room temperature to about 50 ° C. under normal pressure or reduced pressure.

  In the composite metal compound constituting the photocatalyst of the present invention obtained by the above production method, the amount of alkali metal contained does not depend on the washing step, and the type of flux agent, the raw material metal sulfide or the mixture of metal selenide It depends on the relationship of the amount to the amount, the temperature and time at the time of flux, and the amount of alkali metal sulfide or selenide alkali metal salt used as required. According to the above production method, a composite metal compound containing a desired amount of alkali metal can be obtained.

  The MBE film formation is a method of manufacturing by crystal growth by depositing a catalyst component on a substrate under vacuum conditions. As a raw material, metals such as Cu, Ga, In and Zn, and sulfur and selenium can be used. The composition of each raw material is controlled by controlling the evaporation amount on the substrate by defining the evaporation rate in a specific cell. The alkali metal can be introduced using a compound having a vapor pressure, for example, lithium fluoride, sodium fluoride, potassium fluoride and the like.

  Moreover, about the composite metal compound manufactured in this way, it can also be made to contain by adding an alkali metal later. For example, it is a method of mixing an alkali metal compound such as lithium sulfide or sodium sulfide with a composite metal compound obtained in a powder form. It may be mixed in a powder state, or may be a method in which an alkali metal is made into a gaseous state and mixed with a solid powdery composite metal compound.

  Furthermore, an alkali metal can be introduced after the photocatalytic electrode is formed by a process described later.

3. Co-catalyst and surface modification The composite metal compound, which is the photocatalyst of the present invention, generates hydrogen by reducing water using photoexcited electrons, and the co-catalyst functions as an active site. At that time, it is considered that photo-excited electrons give hydrogen molecules to water molecules on the surface of the promoter, thereby generating hydrogen molecules.

  Therefore, in order for the photocatalyst to be used for photohydrolysis to exhibit the photowater splitting activity effectively, it is preferable to use a cocatalyst that promotes hydrogen generation on the photocatalyst surface. In addition, the photoexcited electrons can be efficiently separated by charge and transferred to the cocatalyst supported on the catalyst surface, or the photocatalyst itself can be alleviated from deterioration due to contact with water. It is desirable to modify the surface of the photocatalyst for performance improvement and stability.

  As the promoter in the present invention, noble metals such as platinum, ruthenium, iridium, palladium and gold are preferably used. Two or more cocatalysts may be used, but usually the function of the cocatalyst can be sufficiently exhibited by using only one cocatalyst. The form of supporting these cocatalysts is not particularly limited, but a state where they are supported as particles on the catalyst surface is preferable. The promoter is preferably nano-sized fine particles having an average diameter of 0.1 to 10 nm.

  The method for supporting the cocatalyst is not particularly limited, and examples thereof include general methods such as impregnation, photodeposition, electrophoresis, and sputtering. The amount supported is not particularly limited, and is preferably 0.1 to 10% by mass, and more preferably 0.5 to 3% by mass of the photocatalyst.

  In the impregnation method, a compound that dissolves in water or an organic solvent such as a noble metal halide or an ammine complex is impregnated on a photocatalyst, and then reduced to a metallic state using a reducing agent such as hydrogen. The used water and solvent are removed thermally or by operation under reduced pressure.

  Further, in the sputtering method, normally, a noble metal plate such as platinum (Pt), ruthenium (Ru), iridium (Ir) or the like is collided with an inert gas that has been glow-discharged under vacuum, and the metal that jumps out is photocatalyzed. Adhere to the surface. The photocatalyst is usually subjected to a sputtering method after being processed into an electrode shape.

  There are two types of vapor deposition methods, physical vapor deposition and chemical vapor deposition. In physical vapor deposition, a noble metal such as platinum (Pt), ruthenium (Ru), iridium (Ir), etc. is usually evaporated by heating, and condensed and solidified on the surface of the photocatalyst. The photocatalyst is usually subjected to a vapor deposition method after being processed into an electrode shape. In chemical vapor deposition, volatile compounds including noble metals such as platinum (Pt), ruthenium (Ru) and iridium (Ir) are vaporized and deposited on a photocatalyst, and then reduced using an appropriate reducing agent. To do.

  As surface modification, it is preferable to first laminate or carry a substance that becomes an n-type semiconductor on the above-described composite metal compound. A pn junction is formed by laminating or supporting an n-type semiconductor on the surface of the above-described composite metal compound, which is a p-type semiconductor, whereby excited electrons are transferred from the p-type semiconductor to the n-type semiconductor and further to the promoter. Is carried effectively. At that time, suppression of recombination between excited electrons and vacancies is also expected at the same time, and it is considered that efficient charge separation can be realized.

Examples of the n-type semiconductor preferably used in this embodiment include metal sulfides such as CdS, ZnS, and In ₂ S ₃ , and CdS and ZnS are more preferably used. As such an n-type semiconductor or metal sulfide, two or more kinds may be used, but usually only one kind can sufficiently function. The form of supporting these n-type semiconductor metal sulfides is not particularly limited, but it is preferably in the state of being stacked as a film or supported as particles on the surface of the composite metal compound, and the layer thickness in the case of stacking is usually 0. The particle size in the case of carrying is preferably fine particles having an average diameter of 1 to 50 nm.

  The method for supporting the n-type semiconductor metal sulfide is not particularly limited, and for example, an impregnation method, a chemical solution deposition method (CBD method, chemical bath deposition), photoelectric deposition, electrophoresis, sputtering, etc. are preferably used. It is done. In particular, a chemical solution precipitation method is more preferable.

  The case where CdS is supported by the chemical solution deposition method will be described. Cd salts such as cadmium sulfate and cadmium acetate are preferably used as the Cd source, thiourea is used as the sulfur source, and aqueous ammonia is used as a neutralizing agent. Specifically, the photocatalytic electrode of the present invention is immersed in an aqueous solution containing a Cd salt, thiourea, and aqueous ammonia while being heated to 40 to 80 ° C. Since CdS is deposited on the surface of the electrode, it is immersed for a predetermined time, then taken out and washed with water.

Further, as a surface treatment for imparting stability, it is preferable to stack an oxide such as TiO ₂ or AZO as a film on the electrode surface.

4). Method for Producing Photocatalytic Electrode The photocatalyst of the present invention can be suitably used as a photocatalyst for photowater splitting reaction (for hydrogen production). In that case, the form of the photocatalyst to be subjected to the photohydrolysis reaction is not particularly limited, for example, a form in which the photocatalyst is dispersed in water, a form in which the formed body is installed in water using the photocatalyst as a formed body, and a substrate. A layer comprising a layer containing a photocatalyst is used to form a laminate and the laminate is placed in water, a photocatalyst is immobilized on a current collector to be used as a photocatalyst electrode for a photowater splitting reaction and placed in water together with a counter electrode It is done.

  Among these, the photocatalyst electrode for photo-water decomposition reaction can be produced by, for example, a known method. For example, general methods such as a drop casting method, a particle transfer method, a physical film forming method such as MBE, a roll press method, and an electrophoresis method are preferably used.

  The particle transfer method (Chem. Sci., 2013, 4, 1120-1124) is a preferable method, and a high-performance photocatalytic electrode can be easily produced. That is, a photocatalyst is placed on a first substrate such as glass to obtain a laminate of the photocatalyst layer and the first substrate layer. A conductive layer (current collector conductor) serving as a current collector is provided on the surface of the composite photocatalyst layer of the obtained laminate by vapor deposition or the like. Here, the photocatalyst in the conductive layer side surface layer of the photocatalyst layer is fixed to the conductive layer. Then, a 2nd base material is adhere | attached on the conductive layer surface, and a conductive layer and a photocatalyst layer are peeled from a 1st base material layer. Since a part of the photocatalyst is immobilized on the surface of the conductive layer, the photocatalyst is peeled off together with the conductive layer. As a result, a photohydrolysis electrode having a photocatalyst layer, a conductive layer, and a second base material layer is obtained. Can do.

  In addition, a slurry in which the photocatalyst is dispersed may be applied to the surface of the current collector and dried to obtain a photohydrolysis electrode, or the photocatalyst and the current collector may be integrally formed by pressure molding or the like. The electrode for photohydrolysis reaction may be obtained. Alternatively, the current collector may be immersed in a slurry in which the photocatalyst is dispersed, the voltage is applied, and the photocatalyst may be accumulated on the current collector by electrophoresis.

  For the current collector, a transparent conductive film or glass such as Au, carbon, ITO, or FTO is preferably used. The method for producing the Au or carbon current collector is not particularly limited, but it is preferable that the Au and carbon current collectors are stacked and supported by physical means such as vapor deposition and sputtering.

5. Method for generating hydrogen by photohydrolysis and evaluation of photoelectrochemical properties of photocatalyst electrode The photocatalyst or photocatalyst electrode of the present invention is immersed in water or an aqueous electrolyte solution, and the photocatalyst or photocatalyst electrode is irradiated with light to effect photohydrolysis. By doing so, hydrogen can be produced.

  For example, a photocatalyst is immobilized on a current collector (current collector conductor) made of a conductor as described above to obtain a photocatalyst electrode for hydrogen generation, and the electrodes are connected with a conductive material such as an electric wire. Thereafter, light is irradiated while liquid or gaseous water is supplied to advance the water splitting reaction. The water splitting reaction can be promoted by providing a potential difference between the electrodes as necessary.

  On the other hand, the water splitting reaction may proceed by irradiating light while supplying water to an immobilization product in which the composite photocatalyst is immobilized on an insulating substrate or to a molded body obtained by pressure molding the composite photocatalyst. . Alternatively, the composite photocatalyst may be dispersed in water or an aqueous electrolyte solution, and light may be irradiated to proceed with the water splitting reaction. In this case, the reaction can be promoted by stirring as necessary. In this specification, the composite photocatalyst means a photocatalyst carrying a promoter or surface-modified.

  Although it does not specifically limit as reaction conditions at the time of manufacture of hydrogen, For example, reaction temperature, reaction pressure, etc. can be selected. The reaction temperature is, for example, 0 ° C. or more and 200 ° C. or less, and the reaction pressure is, for example, 2 MPa (G) or less.

  Although the irradiation light depends on the type of photocatalyst, visible light having a wavelength of 350 nm to 1000 nm can be preferably used. Examples of the light source of the irradiation light include the sun, a lamp capable of irradiating approximate sunlight or pseudo-sunlight such as a xenon lamp and a metal halide lamp, a mercury lamp, and an LED.

In addition, the photocatalytic electrode using the photocatalyst of the present invention can have excellent photoelectrochemical properties with a large cathode current density. Specifically, for example, in the case where pseudo-sunlight is irradiated to the photocatalyst electrode prepared under the following conditions under the following conditions, the absolute value is 0.8 mA / cm ² or more at an operating potential of 0.0 V vs RHE, absolute value 1.0 mA / cm ² or more, the absolute value of 1.5 mA / cm ² or more and the absolute value can be 3.0 mA / cm ² or more cathode current density. In addition, for example, in the case where pseudo-sunlight is irradiated under the following conditions to a photocatalyst electrode created under the following conditions, the absolute value is 0.6 mA / cm ² or more at an operating potential of 0.6 V vs RHE, and further the absolute value is 1.0 mA / cm ² or more, the absolute value of 1.5 mA / cm ² or more and the absolute value can be 2.0 mA / cm ² or more cathode current density. The upper limit value of the cathode current density is not particularly limited, but for example, the absolute value can be 30 mA / cm ² or less.

For the evaluation of the photoelectrochemical properties, the above-described photocatalytic electrode, reference electrode (Ag / AgCl, Toyo Sokki Co., Ltd .; TRE-10), and counter electrode (Pt wire) are used as the working electrode. Using a solar simulator (AM1.5G (100 mW / cm ² )) as a light source, measurement is performed using a potentiostat (Hokuto Denko, HSV-110 or HZ-7000) in an electrolytic solution under an argon atmosphere. . Usually, a general technique called cyclic voltammetry (Cyclic voltammetry, CV) is used to measure the response current (photocurrent density) by linearly sweeping the electrode potential. In the evaluation of the electrode for hydrogen generation, a high absolute value of the photocurrent density means high performance, and at the same time, the potential at which the photocurrent density rises is more noble.

  Hereinafter, although the photocatalyst and photocatalyst electrode which consist of the composite metal compound of this invention are demonstrated concretely based on an Example, this invention is not limited to these Examples.

<Example 1>
[Photocatalytic synthesis]
0.6366 g of Cu ₂ S (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.0%) and 0.5655 g of Ga ₂ S ₃ (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.99%) , _{an In} 2 _S 3 (Co. Kojundo Chemical Laboratory, Ltd., purity of 99.99%) to 0.6517G, ZnS and (Co. Kojundo Chemical Laboratory, Ltd., purity of 99.999%) 0.3897G, Then, 0.0084 g of Li ₂ S as a Li source was weighed and mixed in a mortar, and then put into a quartz glass tube sealed at one end. The other end of the quartz glass tube was heated and sealed with a burner while keeping the vacuum. The sealed tube sealed under vacuum was put in an electric furnace and subjected to heat treatment at 800 ° C. for 10 hours (hours). After cooling to room temperature, the contents (hereinafter also referred to as “CGIZS photocatalyst”) were taken out. When the contents were analyzed by ICP, the weight percentages of Li, Cu, Ga, In, Zn, and S were 0.109, 21.9, 14.9, 20.5, 12. 0, 30.5%, and the composition ratios are 0.0331, 0.72, 0.45, 0.38, 0.39, 2.00 (that is, f = 0 in Formula (1)), respectively. 0.031, a = 0.72, b = 0.45, c = 0.38, d = 0.39, e = 0), and the ratio of Li to the total metal atoms is 1.68 mol%. Met.

[Characterization by powder X-ray diffraction (XRD)]
The sample (CGIZS photocatalyst) obtained in Example 1 was subjected to crystal structure analysis using powder X-ray diffraction (XRD). The results are shown in FIG. In the XRD measurement result of FIG. 1, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalytic electrode, particle transfer method]
30 mg of the CGIZS photocatalyst obtained in Example 1 was suspended in 1 mL of 2-propanol, 200 μL of this suspension was dropped on the glass substrate, and then dried three times to form a photocatalyst layer on the glass substrate. Formed. Next, on the photocatalyst layer, Au serving as a current collecting conductor layer was deposited to a thickness of about 2 μm by vapor deposition. As the vapor deposition apparatus, a vacuum vapor deposition apparatus (VPC-260F manufactured by ULVAC KIKOH Co., Ltd.) was used. Then, another glass substrate was adhered from the top of the current collecting conductor layer using a double-sided tape, the first glass substrate was removed, and ultrasonic cleaning was performed in pure water. Finally, a portion other than the photocatalyst layer is sealed with an epoxy resin, and an In conductive wire is bonded to the current collecting conductor layer, so that the photocatalytic layer (CGIZS) / current collecting conductor layer (Au) / glass substrate A CGIZS photocatalyst electrode was obtained.

[CdS surface modification and Pt promoter support]
50 mL of water was heated to 70 ° C., and 0.28 g of cadmium sulfate, 0.4 mL of 28% ammonia water, and 1.4 g of thiourea were sequentially added at the same temperature, and then obtained as described above. Each CGIZS photocatalytic electrode was immersed for 5 minutes. The taken-out photocatalyst electrode was washed with pure water, and then dried at room temperature overnight to obtain a CGIZS photocatalyst electrode modified with CdS. Next, Pt serving as a co-catalyst was supported in an amount corresponding to a thickness of about 1 nm using a multi-film forming apparatus. Thus, a photocatalytic electrode comprising Pt / CdS / photocatalyst layer (CGIZS) / current collecting conductor layer (Au) / glass substrate as an electrode configuration was obtained.

[Electrochemical characteristics evaluation]
Using the photocatalyst electrode obtained by the above [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined under the following measurement conditions. The results are shown in FIG.
・ Light source Solar simulator AM1.5G (100 mW / cm ² )
Electrolyte 0.5M Na ₂ SO ₄ , 0.25M Na ₂ HPO ₄ , 0.25M NaH ₂ PO ₄ pH 6.3
Reference electrode Ag / AgCl, counter electrode Pt wire Argon atmosphere

<Example 2>
[Photocatalytic synthesis]
A CGIZS photocatalyst containing Li was obtained by the same operation as in Example 1 except that Li ₂ S was changed to 0.0001 g. When the obtained CGIZS photocatalyst was subjected to ICP analysis, the weight percentages of Li, Cu, Ga, In, Zn, and S as components were 0.001, 22.7, 15.2, 21.0, respectively. The composition ratios were 0.0002, 0.77, 0.47, 0.40, 0.38, and 2.00, respectively, in order. Moreover, the ratio of Li with respect to all the metal atoms was 0.01 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 2 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 1, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 3>
[Photocatalytic synthesis]
A CGIZS photocatalyst containing Li was obtained in the same manner as in Example 1 except that Li ₂ S was changed to 0.0008 g. When the obtained CGIZS photocatalyst was subjected to ICP analysis, the weight percentages of Li, Cu, Ga, In, Zn and S as components thereof were 0.007, 21.8, 15.5, 21.7, The composition ratios were 0.0023, 0.75, 0.49, 0.41, 0.39, and 2.00, respectively, in order. Moreover, the ratio of Li with respect to all the metal atoms was 0.11 mol%.

[Characterization by XRD]
In the same manner as in Example 1, the XRD measurement of the CGIZS photocatalyst obtained in Example 3 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 1, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 4>
[Photocatalytic synthesis]
A CGIZS photocatalyst was obtained by the same operation as in Example 1 except that Li ₂ S was changed to 0.0126 g. When the obtained CGIZS photocatalyst was subjected to ICP analysis, as components, the weight percentages of Li, Cu, Ga, In, Zn, and S were 0.156, 23.0, 14.6, 20.8, The composition ratios were 0.0486, 0.78, 0.45, 0.39, 0.39, and 2.00, respectively, in order. Moreover, the ratio of Li with respect to all the metal atoms was 2.36 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 4 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 1, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 5>
[Photocatalytic synthesis]
A CGIZS photocatalyst was obtained by the same operation as in Example 1 except that Li ₂ S was changed to 0.0185 g. When the obtained CGIZS photocatalyst was subjected to ICP analysis, the weight percentages of Li, Cu, Ga, In, Zn, and S as components thereof were 0.226, 23.3, 15.2, 20.7, The composition ratios were 0.0721, 0.81, 0.48, 0.40, 0.39, and 2.00, respectively, in order. Moreover, the ratio of Li with respect to all the metal atoms was 3.35 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 5 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 1, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Comparative Example 1>
[Photocatalytic synthesis]
A CGIZS photocatalyst not containing Li was obtained in the same manner as in Example 1 except that Li ₂ S was not used as a raw material. When the obtained CGIZS photocatalyst was analyzed by ICP, the weight percentages of Cu, Ga, In, Zn and S as components thereof were 22.6, 15.1, 20.9, 11.7, 29. The composition ratio was 0.77, 0.47, 0.40, 0.39, and 2.00, respectively. Moreover, the ratio of Li with respect to all the metal atoms was 0.00 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Comparative Example 1 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 1, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 6>
[Photocatalytic synthesis]
A CGIZS photocatalyst was obtained in the same manner as in Example 1 except that 0.0028 g of Na ₂ S was used as the Na source instead of Li ₂ S. When the obtained CGIZS photocatalytic ICP analysis was performed, the weight percentages of Na, Cu, Ga, In, Zn, and S as components were 0.072, 21.7, 15.2, 21.3, and 11 in this order. The composition ratios were 0.0067, 0.73, 0.47, 0.40, 0.39, and 2.0%, respectively, in order. Moreover, the ratio of Na with respect to all the metal atoms was 0.34 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 6 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 3, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 7>
[Photocatalytic synthesis]
A CGIZS photocatalyst was obtained in the same manner as in Example 1 except that 0.0010 g of K ₂ S was used as a K source instead of Li ₂ S. When the obtained CGIZS photocatalyst was analyzed by ICP, K could not be measured due to a detection limit. The theoretical weight% assuming that all the charged K was incorporated into the CGIZS catalyst was 0.03%, and the theoretical value of the ratio of K to all metal atoms was estimated to be 0.04 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 7 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 3, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 8>
[Photocatalytic synthesis]
0.6366 g of Cu ₂ S (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.0%) and 0.5655 g of Ga ₂ S ₃ (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.99%) , _{an In} 2 _S 3 (Co. Kojundo Chemical Laboratory, Ltd., purity of 99.99%) to 0.6517G, ZnS and (Co. Kojundo Chemical Laboratory, Ltd., purity of 99.999%) 0.3897G, As flux agents, 2.29 g of lithium chloride (LiCl, manufactured by Kanto Chemical Co., Ltd., purity 99.9%) and 2.68 g of potassium chloride (KCl, manufactured by Kanto Chemical Co., Ltd., purity 99.5%) After weighing and mixing in a mortar, it was placed in a quartz glass tube sealed at one end. The other end of the quartz glass tube was heated and sealed with a burner while keeping the vacuum. The sealed tube sealed under this vacuum was placed in an electric furnace and heat-treated at 550 ° C. for 15 hours. After cooling to room temperature, the contents (CGIZS photocatalyst) were taken out. The operation of washing the contents with 100 cc of water was performed three times. Thereafter, the filtered product was dried at 40 ° C. for 15 hours. When the obtained CGIZS catalyst was analyzed by ICP, the weight percentages of Li, Cu, Ga, In, Zn, and S were 0.031, 22.7, 15.2, and 21.0, respectively. The composition ratio was 0.0094, 0.76, 0.47, 0.39, 0.36, and 2.00, respectively. Moreover, the ratio of Li with respect to all the metal atoms was 0.47 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the photocatalyst obtained in Example 8 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 5, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 9>
[Photocatalytic synthesis]
A CGIZS photocatalyst was obtained in the same manner as in Example 8 except that the heat treatment conditions were 650 ° C. and 15 hours (hours). When the obtained CGIZS photocatalyst was analyzed by ICP, the weight percentages of Li, Cu, Ga, In, Zn, and S as components were 0.049, 22.6, 15.0, and 21.2, respectively. The composition ratios were 0.015, 0.75, 0.45, 0.39, 0.36, and 2.00, respectively. Moreover, the ratio of Li with respect to all the metal atoms was 0.77 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 9 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 5, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 10>
[Photocatalytic synthesis]
A CGIZS photocatalyst was obtained in the same manner as in Example 8 except that the heat treatment condition was 750 ° C. for 3 hours. When the obtained CGIZS photocatalyst was analyzed by ICP, the weight percentages of Li, Cu, Ga, In, Zn, and S were 0.042, 23.0, 16.4, 20.6, respectively. The composition ratios were 0.0134, 0.81, 0.53, 0.40, 0.39, and 2.00, respectively. Moreover, the ratio of Li with respect to all the metal atoms was 0.63 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 10 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 5, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 11>
[Photocatalytic synthesis]
A CGIZS photocatalyst was obtained in the same manner as in Example 8, except that Ga ₂ S ₃ was changed to 0.6127 g. When the obtained CGIZS photocatalyst was analyzed by ICP, the weight percentages of Li, Cu, Ga, In, Zn, and S were 0.025, 21.5, 16.4, and 20.4, respectively. The composition ratio was 0.0075, 0.71, 0.49, 0.37, 0.36, and 2.00, respectively. Moreover, the ratio of Li with respect to all the metal atoms was 0.39 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the photocatalyst obtained in Example 11 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 5, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 12>
[Photocatalytic synthesis]
A CGIZS photocatalyst was obtained in the same manner as in Example 8, except that Ga ₂ S ₃ was 0.6127 g and the heat treatment condition was 650 ° C. and 25 hr. When the obtained CGIZS photocatalyst was analyzed by ICP, the weight percentages of Li, Cu, Ga, In, Zn, and S as components thereof were 0.087, 22.9, 16.1, and 19.8, respectively. The composition ratio was 0.0266, 0.76, 0.49, 0.37, 0.35, and 2.00, respectively. Moreover, the ratio of Li with respect to all the metal atoms was 1.33 mol%.

[Characterization by XRD]
In the same manner as in Example 1, the XRD measurement of the CGIZS photocatalyst obtained in Example 12 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 5, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 13>
[Photocatalytic synthesis]
A CGIZS photocatalyst was obtained in the same manner as in Example 8, except that 0.7821 g of In ₂ S ₃ and 0.4677 g of ZnS were used. When the obtained CGIZS photocatalyst was subjected to ICP analysis, the weight percentages of Li, Cu, Ga, In, Zn, and S as components were 0.020, 18.4, 13.8, and 22.8, respectively. 13.9 and 31.0%, and the composition ratios were 0.0058, 0.60, 0.41, 0.41, 0.44, and 2.00, respectively. Moreover, the ratio of Li with respect to all the metal atoms was 0.31 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 13 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 5, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 14>
[Photocatalytic synthesis]
0.8038 g of Cu ₂ S (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.0%) and 0.7070 g of Ga ₂ S ₃ (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.99%) In ₂ S ₃ (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.99%) 0.8147 g, and as a flux agent, lithium chloride (LiCl, Kanto Chemical Co., Ltd., purity 99.9%) ) 2.54 g and 2.98 g of potassium chloride (KCl, manufactured by Kanto Chemical Co., Inc., purity 99.5%) were weighed and mixed in a mortar, and then put into a quartz glass tube sealed at one end. The other end of the quartz glass tube was heated and sealed with a burner while keeping the vacuum. The sealed tube sealed under vacuum was put in an electric furnace and heat-treated at 650 ° C. for 15 hours. After cooling to room temperature, the contents (CGIS photocatalyst) were taken out. The operation of washing the contents with 100 cc of water was performed three times. Thereafter, the filtered product was dried at 40 ° C. for 15 hours. When the obtained CGIZS catalyst was analyzed by ICP, the weight percentages of Li, Cu, Ga, In, Zn, and S were 0.0805, 25.6, 18.9, and 25.2 in this order. 0.003 and 30.1%, and the composition ratios were 0.0247, 0.86, 0.58, 0.47, 0.00, and 2.00, respectively. Moreover, the ratio of Li with respect to all the metal atoms was 1.28 mol%.

[Characterization by XRD]
In the same manner as in Example 1, the XRD measurement of the CGIZS photocatalyst obtained in Example 14 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 7, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 15>
Cu ₂ Se ((Ltd.) by Kojundo Chemical Laboratory, purity 99.9%) and _0.8250g, Ga _{2 S} 3 ((Ltd.) by Kojundo Chemical Laboratory, 99.99% purity) and 0.5656g , _{an In} 2 _S 3 (Co. Kojundo Chemical Laboratory, Ltd., purity of 99.99%) to 0.6517G, ZnS and (Co. Kojundo Chemical Laboratory, Ltd., purity of 99.999%) 0.3897G, As a fluxing agent, 2.54 g of lithium chloride (LiCl, manufactured by Kanto Chemical Co., Ltd., purity 99.9%) and 2.98 g of potassium chloride (KCl, manufactured by Kanto Chemical Co., Ltd., purity 99.5%) After weighing and mixing in a mortar, it was placed in a quartz glass tube sealed at one end. The other end of the quartz glass tube was heated and sealed with a burner while keeping the vacuum. The sealed tube sealed under vacuum was put in an electric furnace and heat-treated at 650 ° C. for 15 hours. After cooling to room temperature, the contents (CGIZS photocatalyst) were taken out. The operation of washing the contents with 100 cc of water was performed three times. Thereafter, the filtered product was dried at 40 ° C. for 15 hours. When the obtained CGIZS catalyst was analyzed by ICP, the weight percentages of Li, Cu, Ga, In, Zn, S, and Se as components thereof were 0.0616, 21.3, 13.9, and 19 respectively. .3, 10.3, 22.6, and 12.5%, and the composition ratios are 0.0207, 0.78, 0.46, 0.39, 0.37, 1.64, 0 in order, respectively. .36. Moreover, the ratio of Li with respect to all the metal atoms was 1.02 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 15 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 7, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 16>
A CGIZS photocatalyst was obtained in the same manner as in Example 15 except that 0.5775 g of ZnSe (99.99% manufactured by SIGMA-ALDRICH) was used instead of ZnS. When the obtained photocatalyst was analyzed by ICP, the weight percentages of Li, Cu, Ga, In, Zn, S, and Se as components were 0.0287, 20.0, 12.6, and 17.9, respectively. 9.9, 15.6, 24.1%, and the composition ratios are 0.0106, 0.80, 0.46, 0.40, 0.39, 1.24, 0.76, respectively, in order. Met. Moreover, the ratio of Li with respect to all the metal atoms was 0.51 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 16 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 8, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Preparation of CGIZS photocatalyst electrode, particle transfer method] and [CdS surface modification and Pt promoter support]
In the same manner as in Example 1, [CGIZS photocatalyst electrode production, particle transfer method] and [CdS surface modification and Pt promoter support] were performed.

[Electrochemical characteristics evaluation]
Using the photocatalytic electrode obtained in [CdS surface modification and Pt promoter support], the photoelectrochemical characteristics were examined in the same manner as in Example 1. The results are shown in FIG.

<Example 17>
[Photocatalytic synthesis]
A photocatalyst was synthesized by the flux method. As raw materials, 1.019 g (6.40 mmol) of Cu ₂ S (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.0%), Ga ₂ S ₃ (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99) .99%) 0.905 g (3.84 mmol), In ₂ S ₃ (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.99%) 1.251 g (3.84 mmol), ZnS (Corporation) 0.748 g (7.68 mmol) of a high-purity chemical laboratory, purity 99.999%) was used. In this raw material charge, the composition ratios of Cu, Ga, In, Zn, and S correspond to 0.68, 0.41, 0.41, 0.41, and 2.0, respectively, on a molar basis. The raw materials were mixed in a N ₂ glove box using a menor mortar. LiCl (Kanto Chemical Co., Ltd., purity 99.0%) 4.070 g (48 mmol) and KCl (Kanto Chemical Co., Ltd., purity 99.5%) 4.771 g (32 mmol) were used as fluxing agents. . Mixing of the fluxing agent was performed in the same manner as mixing of the raw material metal sulfide. These mixtures were put in a quartz sheath tube in the order of the raw material and the fluxing agent, and heat-treated at 650 ° C. for 3 hours in the air in a vertical tubular furnace. In the heat treatment, the heating rate is 10 ° C./min. The temperature of the heat treatment was lowered at a rate of 5 ° C./min. The sample after the heat treatment was sufficiently washed with pure water to remove the flux component, and then separated and collected by suction filtration. Then, it was dried overnight at room temperature in the atmosphere. When the obtained dried product (photocatalyst) was analyzed by ICP, the Li content was 0.037 wt%, and the ratio of Li to the total metal atoms was 0.57 mol%.

[Characterization by XRD]
In the same manner as in Example 1, the XRD measurement of the CGIZS photocatalyst obtained in Example 17 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 9, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Cocatalyst support]
With respect to the CGIZS photocatalyst obtained in Example 17, 2% by weight of Ru was supported as a co-catalyst by the photodeposition method. Specifically, light irradiation with a 300 W xenon lamp was performed for 3 hours in a state where 0.2 g of the catalyst powder was suspended in 200 mL of an aqueous solution containing 0.40 mmol of RuCl ₃ and 20 mL of methanol at room temperature. . Thereafter, the mixture was filtered, washed with water, and dried overnight at room temperature.

[Evaluation of hydrogen production activity of CGIZS photocatalyst (suspension system)]
With respect to the CGIZS photocatalyst obtained in Example 17 carrying a Ru promoter as described above, the photocatalytic activity of decomposing water to generate hydrogen was measured from an aqueous solution containing potassium sulfite and sodium sulfide under simulated sunlight irradiation. The hydrogen generation reaction was evaluated. For the evaluation, an upper irradiation type reaction cell connected to a closed circulation type reactor was used. 0.2 g of catalyst powder was suspended in 200 ml of an aqueous solution containing 0.50 mol / L of K ₂ SO ₃ and 0.10 mol / L of Na ₂ S, and stirred during evaluation with a magnetic stirrer. The reaction conditions are a reaction temperature of 20 ° C. and a reaction pressure of 5 kPa. Pseudo sunlight was irradiated from above a Pyrex (registered trademark) glass window using a solar simulator (AM1.5G). The irradiation intensity was 100 mW / cm ² . The generated hydrogen was quantified by an online gas chromatograph (manufactured by Shimadzu Corporation; GC-8A, MS-5A, TCD, Ar carrier). The results are shown in Table 2.

<Example 18>
Except not using In ₂ S ₃ , the composition ratio of Cu, Ga, In, Zn, S was 0.71, 0.43, 0.00, Photocatalysts corresponding to 0.42 and 2.0 were obtained. As a result of ICP analysis, the Li content was 0.048 wt%, and the ratio of Li to the total metal atoms was 0.74 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 18 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 9, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Co-catalyst support] and [Evaluation of hydrogen production activity of CGIZS photocatalyst (suspension system)]
In the same manner as in Example 17, [cocatalyst support] and [hydrogen generation activity evaluation of CGIZS photocatalyst (suspension system)] were performed to evaluate the hydrogen generation activity. The results are shown in Table 2.

<Example 19>
Except not using Ga ₂ S ₃ , the composition ratio of Cu, Ga, In, Zn, and S was 0.71, 0.00, 0.42, and so on, on a molar basis, in the same manner as in Example 17. Photocatalysts corresponding to 0.42 and 2.0 were obtained. As a result of ICP analysis, the Li content was 0.039 wt%, and the ratio of Li to all metal atoms was 0.67 mol%.

[Characterization by XRD]
In the same manner as in Example 1, XRD measurement of the CGIZS photocatalyst obtained in Example 19 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 9, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Co-catalyst support] and [Evaluation of hydrogen production activity of CGIZS photocatalyst (suspension system)]
In the same manner as in Example 17, [cocatalyst support] and [hydrogen generation activity evaluation of CGIZS photocatalyst (suspension system)] were performed to evaluate the hydrogen generation activity. The results are shown in Table 2.

<Comparative example 2>
The photocatalyst was synthesized by solid phase method. Specifically, the same raw material metal sulfide as in Example 17 was used in the same amount, and these mixtures were placed in a quartz glass tube and sealed under a vacuum of 0.5 Pa, Heat treatment was performed at 800 ° C. for 10 hours in a furnace. After standing to cool, it is opened at room temperature, and the powder is taken out. The composition ratios of Cu, Ga, In, Zn, and S are 0.68, 0.41, and 0.41, respectively, on a molar basis. , 0.41 and 2.0 were obtained.

[Characterization by XRD]
In the same manner as in Example 1, the XRD measurement of the CGIZS photocatalyst obtained in Comparative Example 2 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 9, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Co-catalyst support] and [Evaluation of hydrogen production activity of CGIZS photocatalyst (suspension system)]
In the same manner as in Example 17, [cocatalyst support] and [hydrogen generation activity evaluation of CGIZS photocatalyst (suspension system)] were performed to evaluate the hydrogen generation activity. The results are shown in Table 2.

<Comparative Example 3>
The composition ratios of Cu, Ga, In, Zn, and S were 0.71, 0.43, 0.00, and in turn, respectively, on a molar basis in the same manner as in Comparative Example 2 except that In ₂ S ₃ was not used. Photocatalysts corresponding to 0.42 and 2.0 were obtained.

[Characterization by XRD]
In the same manner as in Example 1, the XRD measurement of the CGIZS photocatalyst obtained in Comparative Example 3 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 9, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Co-catalyst support] and [Evaluation of hydrogen generation activity of CGIZS photocatalyst (suspension)]
In the same manner as in Example 17, [cocatalyst support] and [hydrogen generation activity evaluation of CGIZS photocatalyst (suspension system)] were performed to evaluate the hydrogen generation activity. The results are shown in Table 2.

<Comparative Example 4>
The composition ratios of Cu, Ga, In, Zn, and S were 0.71, 0.00, 0.42, 0.42, and 2.0 in the same manner as in Comparative Example 2 except that Ga ₂ S ₃ was not used. Was obtained.

[Characterization by XRD]
In the same manner as in Example 1, the XRD measurement of the CGIZS photocatalyst obtained in Comparative Example 4 was performed. The results are shown in FIG. In the XRD measurement result of FIG. 9, it was confirmed that the sulfide of chalcopyrite type crystal structure was obtained.

[Co-catalyst support] and [Evaluation of hydrogen production activity of CGIZS photocatalyst (suspension system)]
In the same manner as in Example 17, [cocatalyst support] and [hydrogen generation activity evaluation of CGIZS photocatalyst (suspension system)] were performed to evaluate the hydrogen generation activity. The results are shown in Table 2.

  As is clear from FIG. 2 and Table 1, each photocatalyst containing 0.001 to 5 mol% of Li obtained by the solid phase method in Examples 1 to 5 with respect to all metal atoms in the composite metal compound was used. As compared with the photocatalyst electrode produced using the photocatalyst electrode not containing Li in Comparative Example 1, all of the photocatalyst electrodes produced in this manner gave a high cathode current. This is considered to be due to the effect of addition of Li.

  4 and Table 1, the photocatalytic electrode prepared using a photocatalyst containing 0.001 to 5 mol% of Na or K with respect to all metal atoms in the composite metal compound is an alkali in Comparative Example 1. Compared with the photocatalyst electrode produced using the photocatalyst which does not contain, all gave a high cathode current. It is considered that both are due to the effect of addition of alkali.

  Furthermore, in FIG. 6 and Table 1, each catalyst synthesized by the flux method contains 0.001 to 5 mol% Li with respect to all metal atoms in the composite metal compound, and each catalyst is used. All of the photocatalytic electrodes produced in this way have been shown to provide high cathode currents. It is considered that both are due to the effect of addition of Li.

  As is clear from FIG. 8 and Table 1, all of Examples 14 to 16 in which the types of elements were changed within the range of the composite oxide in the present invention gave a high cathode current.

  In addition, as shown in Table 2, Examples 17 to 19 using the composite metal compound in the present invention have a larger amount of hydrogen generation than Comparative Examples 2 to 4 except that no alkali metal is contained. And had an excellent hydrogen production activity. Similarly, it can be said that Examples 1 to 13 and 14 to 16 having the same composition as Example 17 also have excellent hydrogen generation activity.

Claims (3)

A photocatalyst comprising a complex metal compound having a chalcopyrite type crystal structure and capable of generating hydrogen from water using visible light,
The composite metal compound contains Cu, S, at least one of Ga and In, and an alkali metal as essential components, and optionally contains at least one of Zn and Se, and the composite metal compound The photocatalyst which contains the said alkali metal 0.001-5 mol% with respect to all the metal atoms in it.   The photocatalyst according to claim 1, wherein the composite metal compound contains Cu, S, at least one of Ga and In, an alkali metal, and Zn.   A photocatalytic electrode for hydrogen generation, comprising the photocatalyst according to claim 1.

Images